Best Methods to bond 3D Prints Together

3D printing offers unmatched flexibility for creating detailed and complex parts. However, many times, the size or complexity of a project requires joining multiple pieces together, either because the print is too large for the printer bed or to create movable or modular components. Knowing how to glue 3D prints together is essential to producing high-quality results. In this blog post, we'll explore the best methods for gluing 3D prints, including material-specific recommendations, techniques for achieving strong bonds, and tips for clean, seamless finishes.

Best 3D Printer Glue​

The best glue for 3D prints depends heavily on the material of the print and the desired strength of the bond. Below are some of the most effective adhesives categorized by filament type.

1. Cyanoacrylate (Super Glue)

Cyanoacrylate glue, more commonly known as super glue, is one of the most versatile and widely-used adhesives for joining 3D printed parts. It works exceptionally well with PLA, ABS, PETG, and Resin prints. The rapid bonding process of super glue allows for quick assembly, and it provides a reasonably strong bond.

Advantages:

• Easy to apply.
• Dries quickly (within seconds to minutes).
• Strong, rigid bonds suitable for small or medium parts.

Best for: PLA, ABS, Resin, PETG prints.

Tip: Use clamps or rubber bands to hold pieces together while the glue sets for best results.

2. Epoxy Resins

Epoxy adhesives offer much stronger bonds than cyanoacrylate glue, making them a popular choice for large or load-bearing parts. Epoxy typically comes as a two-part system (resin and hardener) and forms an extremely durable bond after curing. Epoxy can bond virtually any type of 3D printing material, including Nylon, ASA, TPU, and Polycarbonate.

Advantages:

• Extremely strong and durable bond.
• Fills gaps between uneven surfaces.
• Works with many types of filaments.

Best for: ABS, PLA, PETG, Nylon, Polycarbonate, TPU, and large 3D prints that require structural integrity.

Tip: Use sandpaper to roughen up surfaces before applying epoxy to improve bonding strength. You can also use clamps to maintain the position of parts while the epoxy cures (usually a few hours).

3. Polyurethane Glue

Polyurethane glue, like Gorilla Glue, is a good choice for bonding Nylon and other flexible or semi-flexible filaments like TPU. It creates a strong, water-resistant bond that is slightly flexible after curing. One of the downsides is that it tends to expand while curing, so care must be taken when applying to avoid excess glue at the joint.

Advantages:

• Suitable for flexible filaments.
• Water-resistant and suitable for outdoor use.
• Strong, slightly flexible bond.

Best for: Nylon, TPU, TPE, flexible filaments.

Tip: Dampen one of the surfaces before applying polyurethane glue to help activate the adhesive and achieve a stronger bond.

4. Hot Glue

Hot glue works in a pinch for less permanent applications or for prototyping, where the bond strength is not critical. While it can be used to join PLA or ABS parts, it does not form a strong, permanent bond compared to other adhesives. It's also not ideal for small, intricate parts because of its bulk and messiness.

Advantages:

• Fast application and curing time.
• Non-toxic and easy to handle.
• Easy to remove or reposition.

Best for: Temporary or non-structural bonding of PLA and ABS parts.

How to Stick Two 3D Prints Together

The process of sticking two 3D prints together involves more than simply applying glue. Preparation and technique are key to achieving a durable and seamless result. Here's a step-by-step guide to bonding two 3D printed parts.

Step 1: Prepare the Surfaces

Before applying any adhesive, it’s essential to ensure the surfaces of the parts are clean and smooth. Use the following tips to prepare the bonding area:

• Clean the surface: Remove any dust, grease, or debris from the surfaces to ensure a good bond. You can use isopropyl alcohol to clean the parts.
• Sanding: Lightly sand the areas to be bonded to roughen the surface, increasing the adhesive’s grip. This is especially important for smooth filaments like PLA and PETG.

Step 2: Apply the Adhesive

• Cyanoacrylate (Super Glue): Apply a small amount of super glue to one part and press the pieces together. Hold them in place for about 30-60 seconds, or use clamps.
• Epoxy: Mix the resin and hardener as per the manufacturer's instructions, then apply a thin layer to one of the parts. Align and press the pieces together, securing them with clamps if needed.

Step 3: Clamp the Parts Together

For a strong bond, keep the parts firmly pressed together using clamps, rubber bands, or a vice. This helps distribute the adhesive evenly and ensures the pieces are aligned correctly during curing.

Step 4: Allow Time to Cure

Each adhesive has a different curing time. Super glue bonds quickly, but epoxy and acrylic solvents may take several hours to fully cure. Follow the manufacturer’s guidelines to ensure the bond reaches full strength.

Strongest Way to Join 3D Prints Together

While adhesives are effective for many applications, there are stronger methods to bond 3D prints together when maximum strength is required.

1. Plastic Welding (Hot Air or Soldering Iron)

Plastic welding is one of the strongest ways to join two 3D printed parts, particularly for materials like PLA and ABS. This method involves melting the edges of both parts, then fusing them together.

• Hot air plastic weldinguses a specialized tool that blows hot air to melt the edges of the parts.
• Soldering iron plastic weldingis more accessible and involves using a standard soldering iron to melt the joint and create a fused bond.

Advantages:

• Creates a seamless bond that’s as strong as the original material.
• No additional adhesives are required.

Tip: After welding, sand and finish the joint to smooth out any imperfections.

2. Mechanical Fasteners (Screws, Bolts, and Inserts)

For large parts or objects that need to withstand mechanical stress, using screws, bolts, or threaded inserts is ideal. This method is commonly used for joining Nylon, Polycarbonate, or other tough filaments.

• Heat-set threaded insertsare particularly useful for adding threaded holes to 3D prints, allowing for secure connections.
• Screws and boltscan be used where strong, removable connections are needed.

Advantages:

• Provides a strong, removable bond.
• Suitable for high-stress parts.

Tip: For best results, design your 3D parts with pre-drilled holes or add threaded inserts after printing.

Securing 3D Printed Parts Together

Securing 3D printed parts together depends on the use case. Some projects require permanent bonds, while others may need modular or temporary connections. Here are a few techniques to secure 3D printed parts.

1. Using Pins or Dowels

If alignment is crucial or you need additional mechanical strength, using alignment pins or dowels can help. Design holes into your parts during modeling, then insert small pins or dowels along the joint line for added reinforcement.

Advantages:

• Improves alignment during gluing.
• Provides additional strength to the bond.

2. Snap-Fit Joints

Snap-fit joints can be integrated directly into the 3D model design, allowing parts to snap together without the need for adhesive. This method is perfect for modular or easily disassembled designs, often used in enclosures, boxes, or clip-on parts.

Advantages:

• No glue or fasteners required.
• Reusable and easy to assemble or disassemble.

3. Magnets

Embedding small magnets in the 3D print during or after the printing process allows parts to be easily secured and detached. This method is often used for enclosures or removable covers.

Advantages:

• Ideal for modular, detachable parts.
• Clean and professional look.

Joining 3D Prints Using Dovetail Joints

Dovetail joints are a mechanical method for joining two parts that can provide both alignment and a strong bond without relying solely on adhesives. This woodworking-inspired technique has been adapted for 3D printing and is especially useful when creating larger or more complex models that need to be printed in multiple parts.

Dovetail joints are designed to interlock, with one piece having a tapered “tail” and the other a matching slot. When properly designed and printed, dovetail joints can be easily assembled and provide a strong, reliable connection between parts. They can be designed directly in CAD software or created in a slicer like PrusaSlicer, which offers tools for splitting models and generating joint patterns.

Why Use Dovetail Joints?

1. Strong Mechanical Bond: Unlike simple glued joints, dovetail joints provide a physical interlock, making them resistant to shear and pull-apart forces.
2. Alignment: The interlocking nature of dovetail joints helps ensure proper alignment between the two parts, minimizing the need for additional clamps or jigs during assembly.
3. Ease of Assembly: Dovetail joints slide together naturally and may only require light adhesive for extra security, depending on the material or the print’s purpose.
4. Modularity: In some cases, dovetail joints can allow for easy disassembly and reassembly, which is helpful for modular or transportable designs.

Designing Dovetail Joints in CAD Software

If you’re designing your own 3D model, you can integrate dovetail joints directly into your model using CAD software like Fusion 360, SolidWorks, or FreeCAD. This method allows you to customize the dovetail joint dimensions and shapes to fit your specific needs. Here's how to go about it:

Steps for Designing Dovetail Joints in CAD:

1. Create the Male Part (Tail): Start by designing the "tail" section, which is typically trapezoidal. The wider part of the trapezoid should be on the outer side to ensure that the parts lock together securely.
2. Design the Female Part (Slot): Next, create the "slot" part, which should be slightly wider than the tail at the top and narrower at the bottom to accommodate the tail and ensure a snug fit.
3. Adjust Tolerances: Since 3D printers have tolerances that may vary slightly depending on the material and print settings, it’s essential to add slight clearance between the tail and slot (usually 0.1-0.3 mm on each side). This ensures the parts fit together properly without being too loose or too tight.
4. Test Fit: After the joint design is complete, it’s a good idea to print a small test piece to verify that the parts fit together smoothly before printing the entire object.

Considerations for CAD-Designed Dovetail Joints:

• Part Orientation: Ensure that the dovetail is oriented in a way that takes advantage of the print’s layer adhesion, as 3D prints are often weaker along the layer lines. For the strongest joint, the dovetail should be designed to minimize stress in the Z-axis (vertical direction).
• Material Properties: Some materials, like PLA, are more rigid and may create very tight joints. For filaments like TPU or Nylon, which have more flexibility, the fit may need to be tighter for a secure connection.
• Layer Height and Detail: The precision of dovetail joints is affected by the layer height used for printing. A finer layer height results in smoother surfaces and a more accurate fit between parts.

Creating Dovetail Joints Using PrusaSlicer

For users who don't want to design dovetail joints from scratch, PrusaSlicer (or similar slicers) offers an alternative: splitting models and adding dovetail joints directly in the slicer. This feature is especially useful when working with large models that need to be printed in multiple pieces due to printer size constraints.

Steps to Add Dovetail Joints in PrusaSlicer:

1. Load the Model: Open your model in PrusaSlicer and prepare it for splitting.
2. Use the Cut Tool: Select the cut tool to split your model into two or more pieces. This is especially useful for large prints that exceed your printer’s build volume.
3. Enable "Add Dovetail Joint": When splitting the model, enable the “Add Dovetail Joint” option from the cut tool settings. PrusaSlicer will automatically add dovetail joints at the split, ensuring that the parts interlock when assembled.
4. Adjust Parameters: You can adjust the size and depth of the dovetail joint in PrusaSlicer’s settings to ensure a good fit for your specific print.
5. Preview the Joint: Use the layer preview to inspect how the dovetail joint will be printed, ensuring that the dimensions and orientation of the joint will result in a secure connection.

Benefits of Using PrusaSlicer for Dovetail Joints:

• No Need for CAD: If you don’t have access to CAD software or prefer not to design joints manually, PrusaSlicer’s built-in tool makes it easy to create dovetail joints with just a few clicks.
• Customizable: You can adjust the dovetail’s parameters directly in the slicer, allowing you to fine-tune the joint for your specific filament, print settings, and model dimensions.
• Supports Large Models: Dovetail joints are an excellent solution for printing large models in sections that are too big to print as a single piece.

Tips for Printing Dovetail Joints

• Print Orientation: When printing dovetail joints, ensure that the tails and slots are aligned properly with the print bed to maximize the strength of the layers. The tail should print flat to the bed whenever possible.
• Layer Adhesion: Use print settings that improve layer adhesion, such as slightly higher print temperatures or lower layer heights. This will help the dovetail joint withstand more mechanical stress.
• Finishing: If the parts don’t fit perfectly due to minor print inaccuracies, you can sand the tail or slot slightly to improve the fit. However, avoid over-sanding, as a loose dovetail joint will not provide a secure connection.

Using Dovetail Joints with Adhesive

While dovetail joints provide a strong mechanical connection, adding adhesive can further strengthen the bond, especially if the joint will be subjected to significant stress or load. Cyanoacrylate (super glue) or epoxy resin can be applied sparingly inside the slot before sliding the tail into place. This hybrid approach combines the interlocking strength of the dovetail with the added security of the adhesive.

Using Threaded Inserts in 3D Prints

Threaded inserts are an excellent solution for adding durable, reusable threads to 3D printed parts, allowing you to fasten components together with screws and bolts. These inserts are particularly useful in applications where the printed part will experience frequent assembly and disassembly, or where strong mechanical connections are required. 3D printed threads, while functional for lightweight applications, are generally not strong enough for repeated use or for handling high loads, especially in materials like PLA and ABS. Threaded inserts solve this problem by embedding metal threads within the plastic, greatly improving durability and strength.

Why Use Threaded Inserts?

1. Durability: The metal threads of an insert are far more wear-resistant than printed plastic threads, ensuring long-term reliability even with frequent use.
2. Increased Strength: Inserts distribute the load more evenly across the part, reducing the risk of thread stripping or part failure under tension or torque.
3. Removability: Screws or bolts can be inserted and removed repeatedly without damaging the part, making threaded inserts ideal for parts that need to be disassembled or adjusted regularly.
4. Versatility: Threaded inserts come in a wide range of sizes and materials, allowing them to be used in almost any 3D printed project.

Types of Threaded Inserts for 3D Prints

There are several types of threaded inserts that can be used with 3D printed parts. The most common types include heat-set inserts, press-fit inserts, and self-tapping inserts.

1. Heat-Set Threaded Inserts

Heat-set threaded inserts are the most popular choice for 3D prints due to their reliability and ease of installation. These inserts are made of brass or stainless steel and are heated and pressed into the plastic, where the heat softens the material and allows the insert to be embedded securely.

Advantages:

• Strong, reliable connection that resists wear and tear.
• Widely available in many sizes (both metric and imperial).
• Excellent for high-strength applications.

How to Install Heat-Set Inserts:

1. Drill or print a hole: Ensure your 3D model includes the correct hole size for the insert. Alternatively, you can drill a hole after printing. The hole should be slightly smaller than the outer diameter of the insert.
2. Heat the insert: Use a soldering iron with a flat tip or a dedicated heat-insert tool to heat the insert. Heat the tip of the soldering iron to around 200°C–300°C, depending on the filament used.
3. Press the insert into place: Once heated, gently press the insert into the hole. The heat will melt the plastic around the insert, allowing it to sink into the part. Ensure the insert is flush with the surface of the print.
4. Allow the plastic to cool: Let the part cool and solidify before using the threads. This process creates a very strong, permanent bond between the insert and the plastic.

Best for: PLA, ABS, PETG, Nylon.

Tip: It’s important to align the insert perfectly when pressing it in. Use a guide or jig if needed to ensure the insert is embedded straight, as misalignment can reduce the strength of the connection.

2. Press-Fit Inserts

Press-fit threaded inserts are designed to be pushed into a pre-sized hole and rely on a tight mechanical fit to stay in place. These inserts do not require heating and can be used in parts printed with tougher materials like Nylon or Polycarbonate, where heat-set inserts may not bond as well due to the higher melting point of the filament.

Advantages:

• Quick and easy to install.
• No heat required, reducing the risk of damaging the print.
• Ideal for high-temperature filaments where heat-set inserts may not be practical.

How to Install Press-Fit Inserts:

1. Drill or print a hole: The hole must be very precise, often within tight tolerances, to ensure a snug fit. The hole should be slightly smaller than the outer diameter of the insert.
2. Press the insert: Using a vice, arbor press, or even a hand tool, push the insert into the hole with consistent pressure. Ensure the insert is seated flush with the surface.

Best for: Nylon, Polycarbonate, TPU, PETG.

Tip: Ensure that the hole is printed or drilled with the right tolerance to ensure a tight fit without overstressing the surrounding plastic.

3. Self-Tapping Inserts

Self-tapping inserts (or self-threading inserts) are designed to cut their own threads into the plastic as they are driven into the part. These inserts are often used for quick fixes or when an existing hole doesn't perfectly match the insert size. They are typically made of metal and have cutting edges that carve into the plastic, creating strong, reusable threads.

Advantages:

• No need for precise hole sizes or special tools.
• Suitable for field installations or retrofitting parts.
• Creates a strong connection in softer plastics.

How to Install Self-Tapping Inserts:

1. Drill a hole: Drill a hole that is slightly smaller than the insert’s outer diameter.
2. Screw in the insert: Use a screwdriver or Allen wrench to twist the self-tapping insert into place. The cutting edges on the insert will create threads as it’s driven into the part.

Best for: PLA, ABS, PETG.

Tip: Self-tapping inserts are best used for applications where high precision isn’t required, but you need a durable, reusable thread quickly.

Design Considerations for Threaded Inserts

When using threaded inserts in your 3D printed design, a few key considerations will help ensure optimal results:

1. Hole Size: If you're designing your own model in CAD, make sure to specify the correct hole size for the insert. This varies depending on the type of insert and filament used. Most manufacturers provide sizing charts that specify the ideal hole diameter for each insert size.
2. Wall Thickness: The area surrounding the insert should be thick enough to withstand the forces applied when the insert is installed and when bolts are torqued down. As a rule of thumb, the wall should be at least twice the diameter of the insert. If the walls are too thin, the plastic may crack or deform.
3. Part Orientation: To maximize the strength of the insert’s bond, orient your print so that the layers run perpendicular to the forces being applied by the screw or bolt. Layer adhesion is weakest along the Z-axis, so avoid orienting the part in a way that would subject the insert to forces parallel to the layers.
4. Heat-Set Insert Boss Design: When using heat-set inserts, it’s a good idea to include a small recess or "boss" around the hole. This helps guide the insert into place and prevents excess plastic from deforming or extruding out of the joint during installation.

Applications of Threaded Inserts in 3D Printing

Threaded inserts greatly expand the range of potential applications for 3D printed parts. Some common uses include:

• Mechanical Assemblies: In robotics, drones, and machinery, where parts need to be securely fastened together and taken apart regularly, threaded inserts provide durability that 3D printed threads can’t match.
• Enclosures: For electronics enclosures, threaded inserts offer a reliable way to secure lids and panels with screws without damaging the threads over time.
• Prototyping: During prototyping, components often need to be modified and reassembled multiple times. Inserts allow you to test and iterate without degrading the integrity of the part.
• Wearable Devices: Threaded inserts provide strong and reliable mounting points for accessories, like straps, clasps, or sensors.

FAQs

What is the best glue for 3D prints together?

The best glue depends on the filament type. For general use, super glue (cyanoacrylate) works well for PLA, ABS, PETG, and resin. Epoxy resin is ideal for a more durable and strong bond across various filament types.

How do you stick two 3D prints together?

To stick two 3D prints together, clean and sand the surfaces, apply the appropriate adhesive (like super glue or epoxy), and clamp the parts together until the adhesive cures. Optionally, for stronger bonds, consider plastic welding or mechanical fasteners.

What is the strongest way to join 3D prints together?

Plastic welding, either with hot air or a soldering iron, offers the strongest bond for 3D prints. Using epoxy resin or threaded inserts with screws can also provide durable and mechanically strong connections.

How do you secure 3D printed parts together?

To secure 3D printed parts, use adhesives for permanent bonding, or mechanical fasteners like screws and threaded inserts for removable connections. You can also use pins, dowels, or magnets for additional security or modular designs.